Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then collects residual toner not transferred and remaining on the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
The fixing device used in such image forming apparatuses may employ a fixing rotary body (e.g., a roller, an endless belt, or an endless film) heated by a heater and a pressing rotary body (e.g., a roller or a belt) pressed against the fixing rotary body to form a fixing nip therebetween through which the recording medium bearing the unfixed toner image is conveyed. As the recording medium passes through the fixing nip in a state in which the front side of the recording medium that bears the unfixed toner image contacts the fixing rotary body, the fixing rotary body heated by the heater and the pressing rotary body apply heat and pressure to the recording medium, thus melting and fixing the toner image on the recording medium. In duplex printing, the recording medium is reversed after it is discharged from the fixing device and then conveyed through the fixing nip again in a state in which the back side of the recording medium that bears the unfixed toner image contacts the fixing rotary body and the front side of the recording medium that bears the fixed toner image contacts the pressing rotary body. Thus, the fixing rotary body and the pressing rotary body fix the toner image on the back side of the recording medium.
In duplex printing, it is important to prevent overheating of the pressing rotary body, which may cause failures described below. For example, if the surface temperature of the pressing rotary body is excessively higher than the surface temperature of the fixing rotary body, the gloss level of the toner image formed on the front side of the recording medium may be different from the gloss level of the toner image formed on the back side of the recording medium or minute scratches on the surface of the pressing rotary body may damage the toner image formed on the recording medium. These failures are conspicuous when glossy paper or coated paper in increasing demand is used as the recording medium.
To address this circumstance, the fixing device may incorporate a fan that produces airflow inside a housing of the fixing device, which impinges on the surface of the pressing rotary body to cool it. However, airflow may also impinge on a temperature detector that should be protected against airflow to detect the surface temperature of the pressing rotary body precisely, resulting in erroneous detection and malfunction of the temperature detector.
Alternatively, the fan may blow air on the pressing rotary body through an intake duct. However, airflow from an outlet of the intake duct may be directed to the temperature detector disposed downstream from the intake duct in the rotation direction of the pressing rotary body upon impingement on the pressing rotary body, resulting in erroneous detection and malfunction of the temperature detector. Moreover, airflow from the intake duct may not be directed to an exhaust duct disposed upstream from the intake duct in the rotation direction of the pressing rotary body through which airflow is exhausted to the outside of the fixing device, but directed to a component (e.g., a cleaner that cleans the pressing rotary body) disposed upstream from the exhaust duct in the rotation direction of the pressing rotary body.
Accordingly, airflow heated by the pressing rotary body upon impingement thereon may leak from an airflow path extending from the outlet of the intake duct to an inlet of the exhaust duct and diffuse to the components other than the pressing rotary body. Consequently, the pressing rotary body may be cooled by airflow inefficiently and the diffused airflow may overheat the components other than the pressing rotary body, resulting in malfunction of the overheated components and coagulation of toner of the toner image that degrades the quality of the toner image.